1. Field of the Invention
The invention is related to abrasive-flow machining and, more particularly, an abrasive-flow machining apparatus, capable of processing an orifice within a part by using either a high-viscosity media, a low-viscosity media, or a media having a viscosity therebetween. The invention is also directed to a method for such processing.
2. Description of the Related Art
Abrasive-flow machining is the process of polishing or abrading a workpiece by passing a viscous media having abrasive particles therein under pressure over the workpiece or through an orifice extending through the workpiece. For purposes of this discussion, media will be discussed as having high viscosity, in the range of between 150-1,000,000 centipoise and media having low viscosity, in the range of 1-150 centipoise. However, the distinction between low-viscosity and high-viscosity may not occur precisely at 150 centipoise and it should be appreciated that such a distinction is made to promote understanding of the subject invention. One example of high-viscosity media is a visco-elastic plastic media such as a semisolid polymer composition. One example of a low-viscosity media is a liquid abrasive slurry that includes abrasives suspended or slurried in fluid media such as cutting fluids of honing fluids. The fluid may have a rheological additive and finely divided abrasive particles incorporated therein. The rheological additive creates a thixotropic slurry.
In the past, abrasive-flow machining for high-viscosity media was performed using one type of abrasive-flow machine and abrasive-flow machining for low-viscosity media was performed utilizing an entirely different abrasive-flow machine.
In particular, high-viscosity media requires higher pressures for mixing and for flowing over or through a workpiece. Pressures in the range of 4,000 psi may be necessary for proper flow of high-viscosity media through the orifice of a workpiece. Additionally, high-viscosity media are typically thixotropic, which means the specific viscosity of the media is dependent upon the shear imparted to the media. In many applications, a pre-specified viscosity is required and, therefore, the high-viscosity media must be treated to satisfy that specific viscosity value. Conditioner stations accomplish this task by subjecting the high-viscosity media to shear until the desired viscosity is obtained. However, such desired viscosity may require pressures in excess of 800 psi to produce the desired shear and thereby obtain the desired viscosity.
Finally, the volume of high-viscosity media that must pass through the orifice of the workpiece to accomplish the desired result is typically less than the volume of low-viscosity media that may be passed through the same orifice to accomplish a desired result. Therefore, while high-viscosity media requires higher pressures for both conditioning the media and processing the workpiece, the volume of fluid necessary for such a task is less than for a low-viscosity media operation. It can then be appreciated that for a high-viscosity media, higher pressures and lower volumes dictate sizing of equipment in a specified manner.
On the other hand, when mixing and flowing a low-viscosity media, low pressures but high volumes are normally required. As an example, conditioning a low-viscosity media may be accomplished using pressures on the order of 150 psi, and such conditioning is intended to mix abrasive particles within the low-viscosity media to provide a homogenous mixture. Such low-viscosity conditioning is different from conditioning of high-viscosity media, which requires imparting shear to adjust the viscosity level of the media. Additionally, to force the low-viscosity media through the orifice of a workpiece, pressures on the order of 1,500 psi may be necessary.
When using a high-viscosity media to process the orifice of a workpiece, it has been found that accurate control of the volume of media through the orifice of the workpiece is a very effective manner of determining when the orifice has been sufficiently processed. This method may also be used for processing low-viscosity medium. Additionally, for low-viscosity media, the media may be applied to the orifice of a workpiece under constant pressure and the flow rate is monitored until a target flow rate is obtained, at which time the process is terminated. In the alternative, the media may be applied to the orifice of the workpiece at a fixed flow rate and the pressure monitored until a target pressure is obtained, at which time the process is terminated. Therefore, not only are the pressures and volumes different between low-viscosity and high-viscosity media processing, but the techniques for measuring and terminating these processes may also be different.
FIG. 1 illustrates a nozzle 1 having an orifice 2 extending through the wall 3 of the nozzle. The nozzle has a first end 4, and a second end 6. The orifice 2 has a wall 8 along its length. The behavior of high viscosity media when processing the orifice wall 8 is different than the behavior of low-viscosity media. In particular, both low-viscosity and high-viscosity media tend to condition the edges at the first end 4 of the orifice 2, while only high-viscosity media tends to polish the wall 8 from the first end 4 toward the second end 6. While a nozzle 1 having an orifice 2 will be used as an example for the method and apparatus described herein, it should be appreciated the subject method and apparatus may be applied to a wide variety of workpieces having orifices.
In many instances, an individual engaged in abrasive-flow machining has a need to process a part or parts using both high-viscosity media and low-viscosity media and, using the current technology, that user is forced to purchase two separate machines, one dedicated to high-viscosity media and the other dedicated to low-viscosity media. Not only does this contribute to expense, but it requires maintenance of two separate machines and consumes additional space on the factory floor. An abrasive-flow machining apparatus and method is desired to alleviate the need for two separate abrasive-machining apparatus for the use of high-viscosity media and low-viscosity media for processing a workpiece and to provide a single apparatus capable of using both, albeit one at a time, of either high-viscosity media or low-viscosity media for processing a workpiece.
A first embodiment of the invention is a system for abrasive flow machining an orifice in a workpiece wherein the system is capable of using abrasive media having a range of viscosity values, wherein the system is comprised of:
a processing station having a processing pump and a processing pump actuator to drive the pump, wherein the pump is supplied with media and wherein the pump forces media through the workpiece orifice to machine the orifice and wherein the pump is adapted to accommodate one of either
a primary processing piston and a primary processing cylinder, wherein the primary processing piston has a diameter and wherein the primary processing piston is slidingly positioned within a primary processing cylinder or
an alternate processing piston and an alternate processing cylinder, wherein the alternate processing piston has a diameter different than the primary processing piston diameter and wherein the alternate processing piston is slidingly positioned within an alternate processing cylinder, and
wherein the processing pump may utilize the primary processing piston and primary processing cylinder for pumping a low viscosity media through the orifice and may utilize the alternate processing piston and alternate processing cylinder for pumping a higher viscosity media through the orifice.
A second embodiment of the invention is a method of modifying a device used for abrasive flow machining with an abrasive media having a viscosity for forcing the media through an orifice of a workpiece, wherein the device has a processing station comprised of a processing pump and a processing pump actuator and wherein the processing pump has a primary processing pump cylinder and a primary processing pump piston with a primary diameter slidably within the primary cylinder for forcing the media from the processing station into the orifice, wherein the method is comprised of the step of modifying the diameter of the primary processing pump piston cylinder and the primary processing piston to accommodate media of different viscosities.
A third embodiment of the invention is a system for abrasive flow machining an orifice of a workpiece, wherein the system has
a processing station for introducing media through an orifice in a workpiece;
a return station, wherein the return station has a double acting piston and the piston is comprised of a return piston slidable within a return piston cylinder, wherein the piston cylinder with the piston in a retracted position accepts media discharged from the processing station and wherein the piston in the extended position forces media from the return station; and
wherein the piston has a rod attached thereto and each of the piston and the rod have a bore extending therethrough such that when the piston is urged toward the extended position, media is forced through the bore and is directed toward the processing station.